Troubleshooting - Engine has poor performance and poor acceleration

Improper, old, or contaminated fuel

Replace fuel. Top Fuel is recommended.
Glow plug fouled or weak

Check for solid green light on EZ-Start® control box gow plug status LED. Test and/or replace glow plug.
Carburetor incorrectly adjusted

Readjust carburetor to factory break-in settings
Dirty air filter

Clean and relube or replace air filter
Slipper clutch loose

Tighten the slipper clutch
Engine clutch slipping

Replace clutch shoes
Excessive load on the engine

Check for bound drivetrain
2-speed shift point needs adjusting (2-speed vehicles only)

Tighten the shift point adjustment screw clockwise to raise the shift point (shift later) or counterclockwise to lower the shift point (shift sooner).
Stripped or worn spur gears

Replace the spur gear(s) before continuing to run the model.
Carburetor low speed mixture set too rich

Adjust the TRX 2.5/3.3 or Pro .15 Low speed needle setting. See also carburetor care for more information.
Engine excessively worn

Repair or replace engine through the Traxxas Engine Replacement Plan.